First record of true conulariids from the Upper Devonian of Poland

Abstract

Phosphatized remains indisputably belonging to conulariids have been found in the lower Famennian (Upper Devonian) deposits at the Kowala quarry in the Holy Cross Mountains, Poland for the first time. The ornamentation patterns and characteristics of the exoskeleton indicate that the conulariids, represented by at least two incomplete specimens, belong to a single species within the genus? Paraconularia. Some Polish Ordovician fossils previously described as conulariids either do not possess morphological characters seen in conulariids, or are too fragmentary to be confidently assigned to conulariids. Therefore, the fossils reported here not only represent the first documented record of conulariids in the Devonian of Poland, but the first true conulariids ever reported and illustrated from Poland. The exoskeleton of one specimen possesses at least three sublethal injuries. As the host deposit of marly shale originated in deep water, it is possible that the injuries did not result from purely physical factors, but rather from attempted predation. This interpretation is consistent with the fact that the lower Famennian deposits at Kowala preserve other predation-related structures such as fish coprolites, fragmented arthropod cuticle and regurgitated remains.

Introduction

Conulariids are extinct marine organisms with a global distribution and a fossil record ranging from the Ediacaran (Van Iten et al., 2016, Cunningham et al., 2016) to the Late Triassic (e.g., Ivantsov and Fedonkin, 2002, Sendino et al., 2012, Lucas, 2012, Van Iten et al., 2013a). They can be found isolated or in clusters. These fossils are not very common, but sometimes they are found in thousands, as in the Bohemian Basin (with a concentration of about 2000 specimens in only one site of about 100 m², mostly Ordovician), Central Andes, Bolivia (very abundant in the Lower Devonian, Conularienschichten) and Silurian of Gotland (Sweden). Characteristic features of most genera are exoskeletons (thecae) that are elongate pyramidal, four-sided, phosphatic (carbonate-rich apatite, see Bouček and Ulrich, 1929, Moore and Harrington, 1956, Ford, 2011, Vinn and Kirsimäe, 2015, Ford et al., 2016) and bear distinct transverse ribs and sometimes longitudinal files of small tubercles. The aperture was terminated by a closure formed by inwardly folded lappets centered on each of the four faces (Van Iten et al., 2008, Sendino et al., 2011, Ford et al., 2016). Once considered as a problematical fossil taxon having no known relationships to any extant taxa, conulariids have even been placed within a separate phylum (e.g. Babcock and Feldmann, 1986a, Babcock, 1991). But phylogenetic analyses indicated that conulariids are scyphozoan cnidarians (Leme et al., 2008, Van Iten et al., 2016). The cnidarian affinity may also be supported by the preservation of tentacle-like structures extending from the aperture in some Ediacaran specimens from China (Van Iten et al., 2013a). The mode of life of conulariids have long been debated. Although it has been proposed that they may have been planktonic or pseudoplanktonic (see Feldmann and Babcock, 1986, Babcock and Feldmann, 1986b), the general consensus is that they were sessile, benthic organisms (e.g., Rodrigues et al., 2003, Simões et al., 2003, Van Iten et al., 2013b).

In the present paper we report on conulariids found in the Upper Devonian deposits of the Holy Cross Mountains, central Poland. Supposed ‘conulariids’ were previously reported and described from the Ordovician of Poland by Kozłowski (1968) and subsequently cited and figured by Dzik and Pisera (1994). However, the conulariid-like fossils studied by Kozłowski (1968) have morphological elements not seen in true conulariids, such as adapical hollow spines that are connected with the interior of the test, and an apical collar. Babcock (1991) undertook a cluster analysis of the skeletal characters of putative conulariids and found that Kozłowski’s (1968) specimens from Poland were not true conulariids. They lack paired transverse ribs, segmental lines and have a skeleton that was secreted from the outside, i.e. an endoskeleton unlike the exoskeleton found in true conulariids (Fig. 1). In addition, some of these specimens did have circular cross section unlike conulariids. The absence of adapical hollow spines in conventional conulariids, as those described by Kozłowski in Ordovician specimens, cannot be a taphonomic effect as these have only been described in the Kozłowski’s (1968) ‘conulariids’.

Dzik and Pisera (1994) figured a supposed fragment as a conulariid but this is hard to identify as a conulariid rib comparable to those figured by Jerre, 1993, Jerre, 1994. Recently, Kozłowski (2012: 55) mentioned the occurrence of conulariids in Middle Devonian (Eifelian) dolomites from the Bardo Syncline in the Holy Cross Mountains. However, these specimens have neither been described nor illustrated and their status is unclear. Therefore, the specimens reported in this paper are the first true conulariids to be described and illustrated from Poland.